The words “once more”

"For if they escaped not who refused him that spake on earth,

much more shall not we escape, if we turn away from him that speaketh from heaven:
Whose voice then shook the earth: but now he hath promised, “Once more I will shake not only the earth but also the heavens.”[Haggai 2:6] Hebrews 12:25,26

The words “once more” indicate the removing of what can be shaken—that is, created things—so that what cannot be shaken may remain." 

F.D Nichol